A smart key system allows a driver located outside of a vehicle to unlock, lock and start the vehicle without needing to insert a key into a key box of the vehicle or execute a particular manipulation. It further may utilize a smart key, such as an easy-to-carry smart card or a radio communication fob.
As the driver carrying the smart key approaches the vehicle, the vehicle can be automatically unlocked through Low Frequency (LF) communication and Radio Frequency (RF) communication with the smart key, and thus the driver can open the door and start the vehicle without a key insertion process.
Specifically, the smart key system for a vehicle performs i) transmitting an authentication request signal in a LF signal to the smart key, ii) receiving an authentication response in a RF signal from the smart key, and iii) determining whether authentication of the smart key that transmits the authentication response signal is completed. In this regard, due to the limit of transmission range of the LF signal, which has a relatively low frequency band compared to the RF signal, the vehicle can receive the authentication response signal from the smart key only if the smart key exists near the vehicle.
A relay located near the vehicle for gathering a LF signal transmitted from the vehicle through e.g., an antenna, and forwarding the LF signal to the smart key located distant from the vehicle, would enable the smart key to transmit an RF signal directly to the vehicle or enable gathering the RF signal through the antenna and forwarding the RF signal to the vehicle. However, such a process may cause hacking problems for the radio signals.